A complementary metal oxide semiconductor (CMOS) image sensor can be manufactured using the same manufacturing process as a CMOS integrated circuit (IC), driven by a single power source, and mounted within the same chip together with an analog circuit or a logic circuit using a CMOS process. Thus, it has several advantages in that the number of peripheral ICs can be reduced.
For this reason, in recent years, instead of a charge coupled device (CCD) image sensor, a CMOS image sensor has attracted attention as an image sensor.
In a CMOS image sensor, in order to read a pixel signal out to the outside, address control is performed on a pixel array section in which a plurality of unit pixels are arranged, and a pixel signal from each unit pixel is arbitrarily selected.
Further, in a CMOS image sensor, a column analog to digital (AD) converting circuit in which a slope type AD converting circuit is arranged in a column can be used as a circuit for performing AD conversion from an analog pixel signal read from a pixel array section into a digital signal.
In this type of column AD converting circuit, when a processing speed or a frame rate is increased by increasing the number of pixels arranged in the pixel array section, an inclination of a slope of a reference signal RAMP used as a reference voltage (a ramp-like voltage) for AD conversion becomes steeper. Due to this influence, particularly in low-gain or low-gradation (low-bit) reading, an AD conversion point of each column is concentrated on a point of a slope, and thus deterioration of linearity occurs due to the influence of power fluctuation or a vertical streak caused by a quantization error due to low gradation.
As a technique of preventing this phenomenon, the applicant of this application already proposed a technique in Patent Literature 1.
Patent Literature 1 discloses a technique of embedding a noise by increasing a pulse width of a reset pulse of a pixel or adjusting a pulse width of a reset pulse of a comparator at the time of reset reading of a vertical signal line and performing signal sampling in the middle of a setting period of time to input capacitance of a comparator that compares an analog pixel signal with a reference signal RAMP.
Since it is possible to spread a reset level distribution by driving using this technique, it is possible to prevent concentration of energy and suppress a quantization vertical streak caused by a quantization error by varying an operation period of time of a column AD converting circuit.